In Input/output (IO) circuits, large diodes occupying large chip areas are needed for Electro-Static Discharge (ESD) protection. For the ESD diodes, the ability to discharge ESD currents is partially determined by the sizes of the diodes. Accordingly, the diodes are designed as large as possible. Furthermore, required by design rules, the sizes of the anodes and cathodes of the diodes affect the widths of the metal lines directly over the respective anodes and cathodes. Accordingly, to gain good electro-migration performance of the metal lines directly over the diodes, the ESD diodes are designed to have large anode pickup regions and/or large cathode pickup regions, rather than comprising many narrow anode pickup regions and/or narrow cathode pickup regions.
When the process for forming the ESD diodes is integrated with the process for forming Fin Field-Effect Transistors (FinFETs), the large anode pickup regions and/or large cathode pickup regions may be formed by epitaxially growing the pickup regions from semiconductor fins, and the epitaxy regions grown from neighboring fins are merged to form large pickup regions. It has been found, however, that some of the large epitaxy regions may have much smaller thickness than small epitaxy regions that are formed simultaneously. As a result, significant leakage currents were generated in the ESD diodes.